It is known to provide the impeller of a rotary pump with a cutter mounted on its inlet for comminuting solids contained in the transported liquid for the pump so the downstream pipes and devices are not plugged. In these rotary pumps, the impeller shaft normally is supported only adjacent the drive motor, so that the cutter vibrates on the shaft bearing that is near the pump impeller while cutting the solids to small pieces. In addition, during operation of rotary pumps, a radial force is applied on the impeller that thus applies an alternate bending to the impeller shaft. Due to this fact, friction occurs at least between the outer end faces of the rotating blade and the counter surface of the abutting, nonrotating element, as well as often in the outer edge, so that premature wear results. On the side that is diametrally opposite the friction point, the clearance is enlarged and thus, the danger of plugging due to solids that have not been cut is increased.